January, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
159
Chemical Constituents Which Influence Gluten Quality' By Betty Sullivan and Cleo Near RUSSELL-MILLER MILLINGCo.. MISNEAPOLIS, MI".
OR more than a century workers engaged in research I n 1906, Norton5 published the first complete analysis of a on wheat and its products have been trying to account gluten (obtained from a straight durum flour), with a total chemically for the difference in the physical properties of 99.05 per cent, including 4.2 per cent ether extract. No of the so-called strong wheats eminently suitable for bread- one since has found more than one per cent of ether extract making, and the soft, weaker wheats which are not so well from any giuten. I n an analysis of more than ten different adapted for this purpose. Soon after 1745 Bercari2 first glutens from varying sources three years ago, the senior noticed that a protein substance, gluten, remained when the author failed to obtain more than one per cent ether extract starch of wheat flour was removed by a stream of water. (Soxhlet method with anhydrous ether) and more than 93 The gluten test, although imperfect, has been until recent per cent total. Gerum and ?\Ietzer,6 after making determiyears the most important sinale - test, either physical or chem- nations of what were then thought to be all the constituents ical, used as a criterion of of gluten, also failed to apthe baking value of wheats. proach a 100 per cent total. I n late years the protein These authors were of the In the analyses of glutens, from straight flours milled o p i n i o n t h a t the starch determination, being an acin a small experimental mill from strong Marquis formed an absorption comcurate measurement of the wheat and from patent and clear flours milled by a plex with the gliadin-gluq u a n t i t y of nitrogenous long process of milling from the same wheat, the lipoid tenin combination w h i c h material present, has supcontent is shown to be lowest in the gluten of best qualp l a n t e d t h e gluten test. made its accurate estimaity (the patent). The calcium content of the ash of tion difficult. The protein determination, these glutens is highest in the gluten of highest however, though quantita0s b o r n e and Voorhees' strength and decreases with the quality of the gluten. tively accurate, gives no inr e p o r t e d the presence of The potassium and magnesium in ashes vary in the formation as to the baking l e c i t h i n in wheat gluten. opposite direction, their proportion increasing as the q u a l i t y of wheat flours, Working8 showed t h a t tenacity and elasticity of the glutens become less. though i t is generally true lipoids markedly influenced A new method for the determination of the lipoid that high protein flours are gluten quality and that adcontent of glutens as well as wheat and its products is of better quality than those dition of phosphatides to the given, which gives higher results than other methods having a low percentage of flour injured t h e g l u t e n . now in use. nitrogenous material. For a D i l l e solved satisfactorily general idea as to the breadthe difficulties of previous m a k i n g value of wheats. investigators in obtaining a n the physical characteristics of their glutens, whether soft analysis of gluten approximating 100 per cent by finding a and sticky, or strong and elastic, are still most valuable. relatively high percentage of lipoids, as measured by the HertVarious theories have, from time to time, been offered wig neutral extraction method. to account for these differences in the behavior of glutens from Wood and Hardy'o showed that the water used in making wheats of varying strength. Balland, Fleurent. Snyder, gluten tests is of prime importance, and affirmed that gluten Shutt, Gortner and Sharp, and their co-workers have at- has of itself neither ductility nor tenacity, but that these tempted to account for these differences by stressing the im- characteristic properties are imparted by electrolytes. portance of the percentage of gliadin, the ratio of the gliadin to Upson and Calvin," h e r s and Ostwald,l* and Gortner and the glutenin, the physical characteristics of the glutenin, size Doherty13 have also studied extensively the reaction of gluten of gluten particles, etc., but no one of these theories offers when immersed in dilute acid, alkaline, and salt solutions. an adequate explanation. It is also interesting to note in As to the composition of gluten ash and the proportion of this connection that Blish3 and later Cross and Swain4 the various ash elements almost no data are available. have shown that the chemical compositions of the proteins, Gerum and Metzer have reported that the ratio of phosthat is, the percentages of amino acids obtained, of wheats phorus to nitrogen in gluten increased with increasing perof widely varying strength are practically the same. centage of flour extraction. While it is generally recognized that the quality and amount Experimental of gluten indicate the bread-making qualities of wheats, no one has analyzed the glutens from flours varying in strength I n a n effort to see if any differences would appear in the and quality. analyses of glutens from flours of varying strength the As has long been known, gluten does not consist entirely of authors started with a wheat gluten, a patent flour gluten, protein, but contains also starch, fat, and small amounts of and a clear flour gluten milled from the same wheat, since i t is ash and crude fiber. The amount of all these constituents J . A m . Chem. Soc., 28, 8 (1906). varies with the details of manipulation, the temperature and Z . Nahr. Genussm., 46,74 (1923). kind of water used, and the skill of the operator, as well as 7 A m . Chem. J., 15, 392 (1893). * Cereal Chem., 1, 153 (1924). the character of the flour itself.
F
I
~~
6
8
I b i d . , 2, 1 (1925). Proc. Roy. SOL.(London), B81, 38 (1909). l 1 Nebr. Agr. Expt. Sta., Res. Bull. 8 (1916). 12 Kolloid-Z., 25, 82, 116 (1919): 26, 66 (1920). 18 J. Agr. Research, 13, 389 (1918). 8
Received July 19, 1926. 2 C. H.Bailey, "Chemistry of Wheat Flour," 192;. 8 THIS JOURNAL, 8, 138 (1916). 4 I b i d . . 16, 49 (1924) 1
10
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
well known that, though the amount of gluten in a clear flour is higher than that of a patent or straight, the quality of the clear gluten, as well as its bread-making value, is distinctly inferior to the patent (the patent and clear being milled from the same wheat). The patent and clear flours, whose analyses are given in Table I, were milled in a large mill by a long process of purification from a strong, dark, hard spring Marquis wheat grown in North Dakota. The flour used for the wheat gluten was a straight flour milled in a small experimental two-stand roller mill from the same wheat. T a b l e I-Analyses
of Flours5
STRAIGHT FLOUR WHEAT Per cent Percentage yield Lipoids E t h e r extract Dry gluten Gluten quality Protein Ash
3:
P206 am __._ 0
...
3,l5 2.19
...
15:09 2.005 0.3146 0.0667 1.016 n 571
WHEAT Per cent
...
1.96 1.43 14.97 Good 14.24 0.611
... ... ... ...
PATENT
CLEAR
Per cent
Per c e n t
58.00
1.62 1.41 14.49 Very good 14.13 0.482 0.0511 0.0252 0.266 0.1330
12.00 2.64 2.35 18.16 Good 17.76
0.804 0.1035 0.0317 0.4371 0.2108
All results calculated t o d r y basis.
The glutens were dried by heating in a high vacuum a t 110" C. for one hour and then finely ground. Protein was determined by the Kjeldahl-Gunning method. Starch, after hydrolysis with HC1 (sp. gr. 1.125), and precipitation of the proteins, was measured by both the Bertrand and MunsonWalker methods. The factor 0.93 was used for conversion of glucose to starch. Ash was determined by heating in a n electric muffle for 16 hours a t 600" C., and moisture by heating one hour at 130" C. Lipoids were determined by a modification of the Ra~k-Phelps'~and Hertwig's methods. The modified method described in the present paper is more easily manipulated and gives higher results on gluten than the other two methods. It is especially useful for the determination of the lipoid content of dry crude gluten; in both the Rask-Phelps and Hertwig methods the gluten particles cohere so strongly when ether is added after the alcohol extraction that a complete extraction of the lipoids is impossible. The alcohol concentration, 70 per cent, in the Hertwig method was changed to 85 per cent, for less gliadin was extracted thus making the filtrate clearer and rendering unnecessary centrifuging or extra filtrations. Even 85 per cent alcohol carried through some gliadin and starch, but the use of a little ammonia in the alcohol prevented this and a clear extract was obtained. The use of ammonia did not lower the results. NEWMETHODFOR LIPOIDDETERMINATION-Athree-gram sample of finely ground dry gluten is thoroughly mixed with twice its weight of fine pumice stone and transferred to an alundum extraction cylinder (size 69 mm. by 26 mm., porosity 5163RA96). It is important that the cylinder be of the right porosity. It is advisable to place a small piece of cotton in the bottom of the extraction shell and on top of the sample. The alundum cylinder is then placed in a specially constructed Caldwell fat extractor and connected to a small glass condenser and to a 250-cc. Erlenmeyer flask, whlch is placed on a water or steam bath. (Any other fat extraction apparatus would doubtless work equally well.) Sinety cc. of 95 per cent alcohol, 5 cc. of concentrated ammonia, and 5 cc. of water are placed in the flask and refluxed over the sample for 30 minutes. The extraction is stopped for a few moments and the liquid transferred to a beaker. T o the same Erlenmeyer flask are then added 100 cc. of ethyl ether, which is gently refluxed for 2 to 3 hours. At the end of this time the extraction is complete and, after cooling as before, 14
THISJOURNAL, 17, 187 (1925)
16
J. Assoc Ofiicral A g r Chem , 7. 91 (1923)
VOl. 19, No. 1
the ether extract is added to the alcohol extract in the beaker. This liquid is evaporated a t a low temperature just to dryness, taken up with chloroform or carbon tetrachloride, and filtered, if necessary, through a small asbestos pad on a Bertrand filter to remove any small amount of starch or soluble protein particles which might have come through the extraction. This filtration is often unnecessary. The filtrate is evaporated in a tared platinum dish to constant weight in vacuo a t 90" C. The method gives closely agreeing duplicate results. The method is applicable also to flours and ground wheats where, when the lipoid content is under 2 per cent, it is advisable to take a 6- to 7-gram sample thoroughly mixed with 5 grams of finely divided pumice stone. At the end of the extraction, the residual mass of gluten or flour and pumice stone is still finely powdered when dry, and an examination of the residue shows i t to be completely extracted. Discussion
I n Table I1 are given the analyses of three typical glutens. It must again be emphasized that the gluten test is empirical and that the composition of any gluten depends on the character of the flour, the kind of water, whether hard or soft, and in no small measure on the experience and technic of the operator. The glutens employed in these experiments, were all obtained by following, as closely as possible, the same procedure and all were washed with the same water-a deep-well water of medium hardness. A11 three glutens showed exhrole-The water gave the following results upon partial analysis total solids, 380; Ca, 50; M g , 18 p p m. These radicals are combined principally a s the bicarbonates with small amounts as chlondes. Traces of sulfate a r e also present.
cellent strength, the patent being the best as to quality while the clear and wheat glutens were about the same, the clear being slightly "shorter" than the wheat gluten. It is to be noted that on all these three strong glutens, the protein is relatively high, 82.5 to 84.4 per cent, as compared with the 72.67 per cent protein found by Dill in a soft, red, winter wheat flour. The starch varied from 4.75 to 8.79 per cent, curiously enough being higher in the patent than in either the clear or wheat glutens-possibly because the protein of the patent is of such character as to hold more tenaciously larger amounts of starch than the lower grades-though this difference may have been due to some slight unconscious variation in the procedure of washing. It is interesting to note in passing, judging from these analyses as well as from those of Dill and Norton, that where the protein of dry crude gluten is relatively high (over 80 per cent), the starch is comparatively low (between 3 and 9 per cent), while in a gluten containing only 70 per cent protein the starch is higher, sometimes close to 20 per cent. As to moisture, a moisture determination should be made a t the same time as samples are weighed out for the other determinations, since finely divided gluten is extremely hygroscopic. Even when it is thoroughly dried a t 100" C. in vacuo and left in a desiccator overnight it will contain 2 to 3 per cent moisture. The crude fiber on all glutens examined was so small as to make its accurate determination impossible. T a b l e 11-Analyses Per cent PATENT Starch Lipoids Protein Ash Total E t h e r extract
8.79 8.50 82.60 0.71 100.60 0.12
-
of G l u t e n s Per CLEAR cent 4.75 10.58 84,42 0.73
100.48 0.223
MARQUIS Per WHEAT cent 4.91 11.13 82.86 1.14 100.04 0,256
-
A real difference in the analyses of these three glutens of varying quality is found in the lipoid content, as given in
January, 1927
I,VD USTRIAL .LVD ENGINEERING CHEMISTRY
Table 11, the clear and wheat glutens showing over 2 per cent more than the patent. This agrees well with the findings of Working, who proved that the addition of phosphatides t o a flour decreased the quality of its gluten and that when 3 per cent of wheat phosphatide was added the gluten could not be recovered. THEASH OF GLUTEh7-h Table 111 the analyses of the ashes of the glutens are given. Calcium was determined by the volumetric potassium permanganate method, magnesium by the method of B. Schmitz. phosphorus as magnesium pyrophosphate, and potassium by the perchloric acid method. The relatively high percentage of silica and phosphorus is worthy of note. The ash was alkaline, however, as is the ash of all wheat products. The percentage of calcium in gluten increases as the quality of gluten increases, ranging from 9.35 to 15.24. This might be predicted in view of the fact that calcium salts have always been regarded as binders in the washing of gluten and a water with a high perrentage of calcium salts, such as the sulfate, is desirable for this purpose. The percentages of magnesium and potassium in these gluten ashes go in the opposite direction, decreasing as the quality of the gluten increases. All gluten ashes show a small
161
amount of potassium as compared with the potassium contained in the flours themselves, owing to the solubility of potassium salts in general. T a b l e 111-Analyses
CaO
%? Kz0
Si02 and C
of G l u t e n A s h e s
PATENT Per cent
CLEAR Per cent
WHEAT Per cent
15.24 10.62 59.21 6.95 5.43
9.35 13.20 61.75 13.69 2 66
11.45 12.94 57.59 9.06 7.66
100.65
98.70
-
TOTAL 9 7 . 4 5
-
-
Table IV contains the percentages of mineral in flour found in the gluten, as calculated from the preceding tables. in Flour Found in G l u t e n
T a b l e IV-Minerals
CaO MgO
P20, K20
PATENT Per cent
CLEAR Per cent
62.22 21.38 22.90 5.38
38.47 16.91 18.73 8 61
‘
Detection of Hydrogen Peroxide in Beverages Preserved with This Compound’ By Charles D. Howard and Nathan Civen STATE
13OARD O F
HEALTH,CONCORD, AT. H.
HE season of 1926 finds
T
a considerable vogue for carbonated beverages based upon “chocolate” (cocoa). Because of the peculiar difficulties involved by proneness t o spoilage of this type of beverage, the bottlers have found themselves confronted with a problem. It was early discoyered that the old standby, sodium benzoate, although serving well in quantities no larger than the conventional one-tenth of 1 per cent in other types of bottlers’ sirups, is impotent to give results on chocolate in this concentration. This soon led to increasing enormously the added dosage of benzoate. Manufacturers are able to do this under the federal law by virtue of a regulation2 rescinding the original one-tenth of 1 per cent limit and establishing no limit in its place.
Hydrogen Peroxide Substituted for Sodium Benzoate
During the past few months manufacturers of chocolate sirups have largely adopted the use of hydrogen peroxide a s a substitute for benzoate, the peroxide being supplied in separate packages to the bottler under such fanciful and identity-concealing names as “Merchandise A,” “Blending Liquid,” etc. With one exception the authors have found all of them to consist of a 3 per cent hydrogen peroxide solution and to be free from acetanilide. The exception proved to represent a 30 per cent peroxide (“perhydrol”). I n contact with organic materials, hydrogen peroxide tends t o decompose into oxygen and water, so that on theoretical considerations, and assuming that it is not to take the place of cleanly methods, no especial objection would seem to attach to its employment in the manufacture of food. Investigations have indicated, however, that the disappearance of this chemical from the finished beverage is by no means as speedy as its promoters have claimed. 1 1
Received September 20, 1926 L; S Dept A g r , Food Inspectmn Decasaon 104 (March 3, 1909).
Statements as a t first made that the peroxide completely disappears from the sirup within a few minutes after its addition, and that it is impossible of detection by an analysis of the finished beverage have been readily disproved. Objections to the Use of Hydrogen Peroxide
There are grounds for considering the presence of peroxide in these beverages as distinctly objectionable. Not only does the present practice apply to beverages of the carbonated variety, but it is apparently being largely extended to “chocolated milk.” Both classes of beverages are extensively consumed by children. This raises the question whether the free consumption of drinks containing substantial traces of this chemical mag not tend to provoke gastric irritation. Methods for the Detection of Hydrogen Peroxide
A number of methods present themselves for the detec tion of residual hydrogen peroxide. That utilizing bichromate, which has apparently been responsible for the claims for non-detection, has been demonstrated to be valueless as applied to the product in question in the presence of small amounts of peroxide. Other tests have proved worthless for this purpose because of being given by mixtures of cocoa and sugar alone. The ones investigated by the authors have included : (1) starch iodide; (2) p-phenylenediamine; (3) benzidine; and (4) vanadic acid. ,411 of these, which are described in Leach and Winton, “Food Inspection and Analysis,” depend upon a reversal of methods for the detection of heated milk and are based upon the blue color which results from their action upon the peroxidase normal to fresh, unheated milk. I n carrying out these tests 1 to 2 cc. of the reagent, as starch-potassium iodide test solution, are added to about 10 cc. of fresh milk and about 5 cc. of
